BERLIN, Dec. 3 -- The killing of an al Qaeda commander in a U.S.-led operation in a remote corner of Pakistan marks an advance in the struggle to locate and eliminate the network's leadership, which has managed to replenish its ranks after suffering key losses in recent years, counterterrorism officials and experts said Saturday.

Pakistan's president, Gen. Pervez Musharraf, said that Hamza Rabia, a top operational planner for al Qaeda, was killed Thursday in an explosion in a tribal area along the border with Afghanistan. Although there were conflicting reports about the details of Rabia's death, Pakistani intelligence sources said U.S. operatives killed him and four others with a missile fired by an unmanned Predator drone.

Pakistani and U.S. officials described Rabia as a major figure in al Qaeda's murky hierarchy and said he would have been responsible for plotting large-scale attacks against U.S. or European targets. At the same time, however, his rapid rise in the network shows how al Qaeda has been able to regenerate after similar setbacks in the past.

Intelligence officials said Rabia, an Egyptian, had replaced Abu Faraj Libbi, another al Qaeda leader who was captured in Pakistan in May. Libbi had taken over the role held by Khalid Sheikh Mohammed, the architect of the Sept. 11, 2001, attacks in the United States who was also caught in Pakistan, in March 2003.

"It's a success story, but al Qaeda has turned into a multi-headed hydra: you chop off one head and another head takes its place," said Magnus Ranstorp, a specialist on al Qaeda at the Swedish National Defense College in Stockholm. "It's a good thing they got him, but I'm sure there are others in the wings who are ready to play a similar role."

Despite their success in tracking down Rabia, there is no indication that U.S. or Pakistani forces have come closer to locating their biggest targets: al Qaeda founder Osama bin Laden and his Egyptian deputy, Ayman Zawahiri, who are still believed to be hiding in the region.

The Bush administration had no public comment on Rabia's death. In the past, the administration has publicly praised Pakistan as a partner in the fight against terrorism. But U.S. officials have become increasingly frustrated with what they see as limited cooperation from the Pakistani military and intelligence services in the hunt for bin Laden.

In June, CIA Director Porter J. Goss said he had "an excellent idea" where bin Laden was hiding but lamented that the al Qaeda leader had taken advantage of "sanctuaries in sovereign states" beyond American reach. Although Goss did not single out the Pakistani government as the problem, U.S. and European officials said bin Laden had almost certainly taken refuge in the semi-autonomous tribal areas near the Afghan border.

Musharraf has recently acknowledged that he is not eager for bin Laden to be caught in his country, where he is seen as a hero to many and is probably more popular than Musharraf, who seized power in a 1999 bloodless military coup. "One would prefer that he's captured somewhere outside Pakistan, by some other people," he said in an October interview with Time magazine.

Counterterrorism officials and analysts said Pakistan serves not just as a hiding place but as an effective base of operations for al Qaeda and other Islamic radical networks, giving them the ability to plan or carry out attacks around the world.

British investigators have found that some of the suicide attackers responsible for the July 7 subway and bus bombings in London had spent time in Pakistan before the attacks. U.S. officials have also complained that Taliban forces fighting the U.S. military in Afghanistan are able to regroup and find fresh recruits across the border in Pakistan.

"The real point here is that Musharraf is not making any dent in the issue that matters -- which is that the extremists are still operating rather freely in Pakistan and feel as comfortable there as ever," said M.J. Gohel, chief executive of the Asia-Pacific Foundation, a London research institute that specializes in security issues in South Asia. "What you need is to completely eradicate and eliminate the entire extremist infrastructure, but nothing has been done there. What has been done is the capture of individuals now and then to please Washington."

The United States and Pakistan seized a series of high-profile figures in the months immediately following the Sept. 11 attacks. Abu Zubaida, a top al Qaeda recruiter and member of bin Laden's inner circle, was arrested in Faisalabad in March 2002. Ramzi Binalshibh, said to be a key Sept. 11 plotter, was caught in Karachi in September 2002. Six months later, Pakistani agents grabbed Mohammed while he was sleeping in a house in Rawalpindi, not far from the headquarters of the Pakistani military.

The arrests fueled hopes that investigators were closing in on bin Laden and would be able to completely dismantle the al Qaeda central leadership. But in the past two years, the search for ranking al Qaeda figures has sputtered while others have emerged to lead terrorist attacks elsewhere.

In Iraq, for instance, Jordanian fighter Abu Musab Zarqawi has become a leader of the insurgency, pledging loyalty to bin Laden and giving al Qaeda a new base of operations. Al Qaeda has also created affiliates and alliances with regional extremist groups in North Africa, Europe and Southeast Asia.

Rabia was killed Thursday along with four associates in a missile strike in the tribal region of North Waziristan, officials and a witness said Saturday. The incident was first reported by the Pakistani newspaper Dawn, which cited witnesses in asserting that the men had been killed by rockets fired by an unmanned U.S. surveillance drone known as a Predator.

In public statements, Pakistani officials declined to say whether Rabia had been killed by an American missile, although several privately confirmed the report. The use of such tactics is highly controversial in Pakistan, especially in the remote tribal areas where there is strong opposition to the presence of any U.S. military forces.

"Here is what I can tell you: Our troops were not involved in the operation, but this is one of the areas where our intelligence and operational cooperation with U.S. services is most intense," said a senior Pakistani intelligence official in the northwestern city of Peshawar, which is near North Waziristan.

"Comments on media reports that it was a Predator strike would invoke sovereignty issues," the official added. "Let's enjoy the fact that al Qaeda has lost another key person."

Rabia's name does not appear on the FBI's list of most-wanted terrorists. But Pakistani officials described him as a major catch and a close associate of Zawahiri, the second-ranking al Qaeda leader and a fellow Egyptian.

They said Rabia had been the focus of an intense manhunt since the arrest in Pakistan last May of Libbi, a Libyan whom U.S. intelligence sources described at the time as al-Qaeda's third-ranking leader. Libbi and Rabia are suspected of orchestrating two assassination attempts against Musharraf in 2003.

The interrogation of Libbi by U.S. and Pakistani intelligence operatives "confirmed that Abu Hamza Rabia was in touch with Ayman Zawahiri and he was an important connection between Zawahiri and various Al Qaeda cells, at least until last year," said another Pakistani intelligence official who is involved in counterterrorism work in the tribal areas. The official added that contact between Rabia and Zawahiri appears to have ceased during the last several months.

A third Pakistani intelligence official said that for the past few months, Rabia had been "playing hide-and-seek with the Americans, who were on his tail. He was a fast mover who shuttled between the tribal areas and Afghan border areas frequently."

According to Dawn, Rabia died along with four other men, two of them also Arabs, when an explosion destroyed the mud-walled compound where they were staying in the village of Asoray near Miram Shah, the administrative capital of North Waziristan. Local authorities claimed the men died while making bombs. But the newspaper cited witnesses who said the house was destroyed by missiles around 1:45 a.m.

That account was supported by another witness, Zammarud Khan, who runs a grocery store in the village, according to his brother, Wazir, a driver in Karachi. Wazir Khan said in an interview that his brother told him that at least one of the men had just arrived the day before the attack. Following the collapse of Afghanistan's Taliban government in late 2001, al Qaeda members streamed across the border and took refuge among the ethnic Pushtun tribesmen who populate the area. Many subsequently left for other parts of Pakistan, and hundreds have been caught, although some have remained in the tribal region. Earlier this year, a member of al Qaeda, Haitham Yemeni, was killed by a Predator in North Waziristan.

Spokesmen for the U.S. military and the U.S. Embassy in Islamabad said they had no information on Rabia or the circumstances of his death.